Low-sulfer odorants featuring improved stability

ABSTRACT

The present invention relates to an odorant comprising or consisting of
     (A) at least 75% by weight of acrylic acid methyl ester and/or acrylic acid ethyl ester,   (B) 2-19.5% by weight of tetrahydrothiophene (THT),   (C) 5-50 ppm of hydroquinone monomethyl ether,
 
and also neither, one or both components selected from the group consisting of
   (D) 0.025-0.2% by weight of butylhydroxy toluene and/or butyl hydroxyanisole
 
and
   (E) 5-500 ppm of one or more compounds of formula (I)   

     
       
         
         
             
             
         
       
     
     wherein
     R is selected from the group consisting of H, —OH, —NH 2 , —O 2 CR 1  and —NOCR 1 , wherein R 1  represents an alkyl radical containing 1 to 4 carbon atoms,
 
based on the total weight of the odorant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority to PCT/EP2007/060057, filed on Sep. 21, 2007, which asserts priority to DE 20 2006 014 741.1, filed on Sep. 22, 2006, which are incorporated herein by reference in their entireties.

The present invention relates to low-sulfur odorants comprising or consisting of A) acrylic acid methyl ester and/or acrylic acid ethyl ester, B) tetrahydrothiophene (THT) and C) hydroquinone monomethyl ether in specific concentrations. The content of hydroquinone monomethyl ether is in this case very low. In addition to said components A), B) and C), an odorant according to the invention can also comprise one, two or more components having a stabilizing effect, cf. in this regard the information given concerning components D) and E) below. The invention relates also to a corresponding fuel gas (preferably natural gas) having a methane content of at least 60% by weight, which comprises a content of the odorant according to the invention.

A method for odorizing a fuel gas of this type is also described.

The town and coke-oven gases used previously for the public supply of gas contained components having an intensive smell and therefore had a strong inherent smell, so that issuing gas could easily be perceived.

The term “gas odorizing” refers to the addition of substances (odorants) which have an intensive smell and act as warning or alarm substances to gases having no significant inherent smell, i.e. to otherwise substantially or completely odorless gases.

Natural gas consists mainly of methane (typical methane contents lie in the range of from 50 to 99% by weight, usually in the range of from 60 to 99% by weight and conventionally 80 to 99% by weight) and can, depending on their origin, additionally contain differing contents of ethane, propane and hydrocarbons of relatively high molecular weight. Natural gas H(H=high) has a methane content of from 87 to 99.1% by volume, natural gas L (L=low) contains generally 79.8 to 87% by volume of methane.

Owing to its high degree of purity, the gas, conventionally obtained from natural gas, used today in the public mains network is per se almost odorless.

If leakages are not noted in good time, explosive gas/air mixtures having a high risk potential soon build up.

For safety reasons, gas is therefore odorized by adding substances having an intensive smell. Thus, in Germany, for example, all gases which do not have a sufficient inherent smell and are distributed in the public supply of gas must be odorized in accordance with DVGW Worksheet G 280 (DVGW=Deutscher Verein des Gas- and Wasserfaches e.V. (German Technical and Scientific Association for Gas and Water)). These odorants are perceptible even when highly diluted and cause in a desired manner, owing to their exceptionally unpleasant smell, an alarm association in humans. The odorant must not only smell unpleasant and unmistakable, but rather above all be unambiguously a warning smell. Therefore, the smell of the odorized gas may not be a smell with which humans are familiar from everyday life, for example from cooking and the home. In Germany approximately 90% of service gas is currently odorized with tetrahydrothiophene (THT) (12-25 mg/m³); in addition, odorizing with mercaptans is also conventional.

It can be beneficial to add to the gas a relatively large amount of odorant over a relatively long period of time. In the case of what is known as shock odorizing, one to three times the amount of odorant is supplied to the gas, compared to conventional odorizing. Shock odorizing is applied for example during the putting-into-operation of new networks or line portions in order more rapidly to attain the minimum odorant concentration or else to identify small leaks in the gas installation.

THT alone is ideal for reliable odorizing of gas. However, with a view to sensitive treatment of the environment, it should be noted that sulfur oxides are formed as combustion products to a greater degree when gases odorized in this way are burned.

As efforts are generally made to reduce or avoid sulfur compounds, attempts have already been made to develop low-sulfur or sulfur-free odorants.

JP-B-51-007481 mentions that acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate and butyl acrylate are known to have weak odorizing properties for fuel gases and to be almost insignificant in this regard. The document describes and claims allyl acrylate as an effective odorizing component.

JP-A 55-104393 describes that odorants containing an alkyne and at least 2 compounds selected from a group consisting of methyl acrylate, ethyl acrylate, methyl methacrylate, allyl methacrylate, ethyl propionate, methyl-n-butyrate, methyl isobutyrate and prenyl acrylate, and also if appropriate tert-butyl mercaptan, are suitable for odorizing fuel gases. The amount of odorant is, based on weight, 50 ppm (mg/kg of gas), preferably greater than or equal to 100 ppm. The best results in the case of LPG (liquid gas) were obtained with mixtures comprising tert-butyl mercaptan (TBM). By adding 2-butyne (50 ppm) to a mixture of methyl acrylate (50 ppm), allyl acrylate (100 ppm) and TBM (5 ppm), a better odorizing effect was attained. The best result was displayed by a mixture of 2-butyne (50 ppm), allyl methacrylate (20 ppm), methyl acrylate (20 ppm), methyl-n-butyrate (20 ppm), methyl isobutyrate (20 ppm), ethyl propionate (20 ppm) and TBM (5 ppm).

JP-B-51-034841 determined “odor threshold values” of various substances, wherein n-valeric acid, n-butyric acid, isobutyraldehyde and various methyl amines had low olfactory “odor threshold values”. Ethyl acrylate or n-valeric acid used alone did not have a sufficiently odorizing effect. An optimized mixture comprised 50-90% by weight of ethyl acrylate, 10-50% by weight of n-valeric acid and optionally triethyl amine. The mixture which was taken to be most effective comprised ethyl acrylate, n-valeric acid and triethyl amine, wherein this mixture contained equal parts by weight of n-valeric acid and triethyl amine and also 30 to 80% by weight of ethyl acrylate; a corresponding mixture consisting of 60% by weight of ethyl acrylate and 20% by weight of each of n-valeric acid and triethyl amine was added to a gaseous fuel gas at 10 mg/m³.

Odorants for fuel gases consisting of ethyl acrylate (70% by weight) and tert-butyl mercaptan (30% by weight) are known from JP-B 51-021402. This mixture was added to a gaseous fuel gas in an amount of 5 mg/m³.

Odorous substances for odorizing heating gases consisting of a) 30-70% by weight of C₁-C₄ alkyl mercaptans, b) 10-30% by weight of n-valeraldehyde and/or isovaleraldehyde, n-butyric acid and/or isobutyric acid and also if appropriate c) up to 60% by weight of tetrahydrothiophene (THT) are described in DE-A 31 51 215. These odorants were added to heating gas in amounts of from 5-40 mg/m³.

In DE-A 198 37 066 the problem of sulfur-free gas odorizing was solved by means of mixtures containing at least one acrylic acid C₁-C₁₂ alkyl ester and a nitrogen compound having a boiling point in the range of from 90 to 210° C. and a molecular weight of from 80 to 160, wherein mixtures containing at least two different acrylic acid alkyl esters are preferred. Alkyl-substituted 1,4-pyrazines are described as being particularly suitable nitrogen compounds.

Mixtures containing a) 1 proportion by weight of dimethyl sulfide, b) 0.8-3 proportions by weight of tert-butyl mercaptan and c) 0.1-0.2 proportions by weight of tert-heptyl mercaptan or 0.05-0.3 proportions by weight of tert-hexyl mercaptan for odorizing fuel gases are known from JP-A 61-223094. These mixtures had a smell of tert-butyl mercaptan which is associated with the smell of the town gas.

The use of norbornene derivatives for fuel gas odorizing is known from JP-A55056190. LPG was mixed at 40 mg/kg with a mixture of equal parts of 5-ethylidene-2-norbornene and 5-vinyl-2-norbornene or at 50 mg/kg with a mixture of 80% by weight of 5-ethylidene-2-norbornene and 20% by weight of ethyl acrylate.

Mixtures for odorizing town gas containing norbornene or a norbornene derivative and a diluting agent are described in DE-A 100 58 805.

Mixtures of C₄-C₇ aldehydes and sulfur compounds are described as odorants in JP-A 50-126004. The odorizing of 1 kg of propane was carried out with 50 mg of a mixture of 60% by weight of valeraldehyde and 40% by weight of n-butyl mercaptan. Valeraldehyde strengthens in this case the smell of the n-butyl mercaptan. 2-Methylvaleraldehyde was used in a similar manner.

U.S. Pat. No. 4,487,613 proposes odorants for fuel gases having a high content of sulfur-containing compounds, which additionally contain the warning smell-strengthening compounds 2-methoxy-3-isobutyl pyrazine and/or 4-methyl-4-mercapto-2-pentanone. The odorants disclosed in accordance with U.S. Pat. No. 4,487,613 can also contain low contents of acrylic acid methyl ester.

WO 2005/061680 describes the use of a mixture containing (a) at least two different acrylic acid C₁-C₆ alkyl esters, (b) at least one compound from the group of the C₁-C₈ mercaptans, the C₄-C₁₂ thiophenes, the C₂-C₈ sulfides or the C₂-C₈ disulfides and (c) at least one compound from the group of the norbornenes, the C₁-C₆ carboxylic acids, the C₁-C₈ aldehydes, the C₆-C₁₄ phenols, the C₇-C₁₄ anisoles or the C₄-C₁₄ pyrazines and also if appropriate (d) an antioxidant for odorizing fuel gas having a methane content of at least 60% by weight.

WO 2005/103210 relates to odorants and accordingly odorized gases comprising

-   -   (i) 0.1-49.9% of a cyclic or open-chain thioether containing at         most 9 carbon atoms,     -   (ii) 50-99.8% of an acrylic acid C₁-C₁₂ ester,     -   (iii) 0.001-0.1% of specific nitroxides.

The mixtures proposed in accordance with WO 2005/103210 are said to be allegedly improved odorants. WO 2005/103210 states in this regard inter alia that the nitroxides proposed therein effectively prevent the radical polarization, which is of course to be avoided in the case of odorants, of the acrylic acid esters contained therein. WO 2005/103210 regards mixtures comprising ethyl acrylate and THT as being particularly preferred.

However, the nitroxides proposed in accordance with WO 2005/103210 alone do not cause completely sufficient stabilization of the odorant in question. Thus, interactions can occur between the nitroxides and the thioethers, in particular in the presence of metals and metal surfaces, such as for example in the vessels for storing the odorants, so that the warning smell of the odorants proposed therein can change and become impaired. As a result of interactions of the nitroxides with metals and metal surfaces, consumption can also occur as a result of abreaction of the nitroxides, so that comprehensive stabilization of the acrylic acid esters is no longer ensured in each case. Thus, nitroxides can be oxidized in the presence of copper ions (to form the corresponding nitrons) or reduced in the presence of iron ions (to form the corresponding N-hydroxy compounds).

Alternative low-sulfur odorants for odorizing natural gas or fuel gases consisting mainly of methane, which are preferably superior in their properties to the previously known odorants, were therefore sought, wherein, in addition to the quality of the warning smell, the stability in storage of the odorant is also important, so that the quality of the warning smell can be ensured even over a relatively long period of (storage) time.

The subject-matter of the present invention is a mixture (referred to hereinafter as an “odorant”) comprising or (substantially) consisting of the following components:

-   (A) at least 75% by weight of acrylic acid methyl ester and/or     acrylic acid ethyl ester, -   (B) 2-19.5% by weight of tetrahydrothiophene (THT), -   (C) 5-50 ppm of hydroquinone monomethyl ether,     and also neither, one or both components selected from the group     consisting of -   (D) 0.025-0.2% by weight of butylhydroxy toluene and/or butyl     hydroxyanisole     and -   (E) 5-500 ppm of one or more compounds of formula (I)

wherein R is selected from the group consisting of H, —OH, —NH₂, —O₂CR¹ and —NOCR¹, wherein R¹ represents an alkyl radical containing 1 to 4 carbon atoms, based on the total weight of the odorant.

Also relevant in practice is a corresponding method for odorizing fuel gases having a methane content of at least 60% by weight (of preferably natural gas) using an odorant according to the invention. In this case, an odorant according to the invention is added to the fuel gas. With regard to preferred configurations, reference is made to the information given concerning the preferred odorants according to the invention and the uses thereof, which applies accordingly.

A further subject-matter of the present invention is a fuel gas having a methane content of at least 60% by weight comprising an odorant according to the invention. With regard to the preferred odorants for use in fuel gases according to the invention, reference is made to the subsequent discussion of preferred odorants.

The fuel gas to be odorized or the fuel gas according to the invention has a methane content of at least 60% by weight, preferably of at least 70% by weight and particularly preferably of at least 75% by weight.

The total amount of acrylic acid methyl ester and acrylic acid ethyl ester (component (A)) in the odorants according to the invention is at least 75% by weight, preferably at least 84% by weight.

In so far as the odorants according to the invention comprise acrylic acid methyl ester and acrylic acid ethyl ester, the preferred ratio by weight of acrylic acid methyl ester to acrylic acid ethyl ester lies in the range of from 9:1-1:9, preferably in the range of from 7:3-3:7, in particular in the range of from 3:1-1:4. Most particularly preferably, the ratio by weight of acrylic acid methyl ester to acrylic acid ethyl ester lies in the range of from 1:1-1:3.

The compound tetrahydrothiophene (component (B)) is contained in the odorants according to the invention at 2-19.5% by weight, preferably at 5-15% by weight.

The compound hydroquinone monomethyl ether (4-methoxyphenol, MeHQ) (component (C)) is contained in the odorants according to the invention in very low amounts lying in the range of from 5-50 ppm, preferably 10-20 ppm. The use of larger amounts of component (C) is surprisingly not required to attain high stability of the odorant; the use of the low amount provided in accordance with the invention of component (C) is advantageous for stability reasons, in particular if component (E) is present (cf. also the examples).

Odorants according to the invention preferably comprise

as component (D) 0.025-0.2% by weight of butylhydroxy toluene and/or butyl hydroxyanisole and/or as component (E) 5-500 ppm of one or more compounds of formula (I)

wherein R is selected from the group consisting of H, —OH, —NH₂, —O₂CR¹ and —NOCR¹, wherein R¹ represents an alkyl radical containing 1 to 4 carbon atoms.

In so far as they are contained, the total amount of the compounds of component (D) butylhydroxy toluene (BHT, ionol, 2,6-di-tert-butyl-p-cresol, E 321) and/or butyl hydroxyanisole (BHA, E 320) in the odorants according to the invention lies in the range of from 0.025-0.2% by weight, preferably in the range of from 0.05-0.15% by weight.

Owing to the presence of component (C), in particular in combination with one or both further components (D) and/or (E), there is attained in particular high stability in storage of the odorants according to the invention and also of an odorized fuel gas according to the invention. Stability in storage tests have shown that the warning smell of odorants according to the invention in a fuel gas remains substantially constant over a period of more than 8 months at 40° C. (incubator), cf. also the examples below. Particularly high stability in storage is attained if component (C) and one of components (D) and/or (E) are at the same time present.

The total amount of component (E) in preferred odorants according to the invention lies in the range of from 5-500 ppm, preferably in the range of from 10-200 ppm. The compounds of formula (I) are stable nitroxides.

The synthesis of stable nitroxides of formula (I) is described in detail in the literature, for example in Chem. Rev. 1978, 78, 37, Synthesis 1971, 190 and “Synthetic Chemistry of Stable Nitroxides”, L. B. Volodarsky et al., CRC Press, 1993, ISBN:0-8493-4590-1.

Preferred compounds which can be used in component (E) correspond to formula (I) wherein R═H (2,2,6,6-tetramethylpiperidin-1-oxyl of formula (Ia), known under the abbreviation TEMPO) or wherein R═OH (corresponding to formula (Ib)) and are commercially available.

The amount of odorant based on the fuel gas to be odorized lies typically in the range of from 2-100 mg/m³, preferably 3-50 mg/m³, particularly preferably 5-40 mg/m³ and most particularly preferably 8-35 mg/m³.

Preferably, the odorants according to the invention and the fuel gases, in particular natural gas, containing these mixtures contain, in addition to THT (component (B)), neither tert-butyl mercaptan (TBM) nor ethyl mercaptan. Preferably, the odorant comprises no mercaptan at all. Particularly preferably, apart from tetrahydrothiophene (component (B)), no further sulfur-containing compound is contained in the odorant according to the invention.

Preferred odorants according to the invention comprise or consist of:

-   (A) at least 84% by weight of acrylic acid methyl ester and/or     acrylic acid ethyl ester,     and/or -   (B) 5-15% by weight of tetrahydrothiophene (THT),     and/or -   (C) 10-20 ppm of hydroquinone monomethyl ether,     and/or -   (D) 0.05-0.15% by weight of butylhydroxy toluene and/or butyl     hydroxyanisole     and/or -   (E) 10-200 ppm of one or more compounds of formula (I).

Particularly preferred odorants according to the invention comprise:

-   (A) at least 84% by weight of acrylic acid methyl ester and/or     acrylic acid ethyl ester, -   (B) 5-15% by weight of tetrahydrothiophene (THT),     and -   (C) 10-20 ppm of hydroquinone monomethyl ether -   and also neither, one or both components selected from the group     consisting of -   (D) 0.05-0.15% by weight of butylhydroxy toluene and/or butyl     hydroxyanisole     and -   (E) 10-200 ppm of one or more compounds of formula (I).

Particularly preferably, an odorant according to the invention comprises

-   (A) at least 84% by weight of acrylic acid methyl ester and/or     acrylic acid ethyl ester, -   (B) 5-15% by weight of tetrahydrothiophene (THT),     and -   (C) 10-20 ppm of hydroquinone monomethyl ether and also one or both     components selected from the group consisting of -   (D) 0.05-0.15% by weight of butylhydroxy toluene     and -   (E) 10-200 ppm of one or more compounds of formula (I)

wherein R is selected from the group consisting of H and —OH.

The particularly preferred mixtures are distinguished by particularly high stability in storage. Partly synergistic stability improvements are observed in odorizings according to the invention on combination of hydroquinone monomethyl ether (component (C)) and at least one further component (D) and/or (E).

In so far as one or more compounds of formula (I) are contained as component (E) in an odorant according to the invention, said compounds do not display the above-discussed drawbacks of the odorants proposed in accordance with WO 2005/103210; presumably, this is due to the presence of component (C), that is to say, the presence of the low amount of hydroquinone monomethyl ether.

Most particularly preferred odorizings according to the invention contain or consist of

-   (A) at least 84% by weight of acrylic acid methyl ester and/or     acrylic acid ethyl ester, -   (B) 5-15% by weight of tetrahydrothiophene, -   (C) 10-20 ppm of hydroquinone monomethyl ether,     and -   (D) 0.05-0.15% by weight of butylhydroxy toluene.

Alternative most particularly preferred odorizings according to the invention contain or consist of

-   (A) at least 84% by weight of acrylic acid methyl ester and/or     acrylic acid ethyl ester, -   (B) 5-15% by weight of tetrahydrothiophene, -   (C) 10-20 ppm of hydroquinone monomethyl ether,     and -   (E) 10-200 ppm of one or more compounds of formula (Ia) or (Ib).

With these most particularly preferred odorants, the best odorizing of the gas and in particular the highest stability of odorants according to the invention and fuel gases according to the invention were attained. The warning smell was most strongly pronounced and was perceived still clearly and in substantially unadulterated form even after a storage time of well over 8 months.

The present invention relates also to a vessel comprising:

(i) an odorant according to the invention comprising component (E), wherein the odorant or (ii) a fuel gas according to the invention, containing an odorant comprising component (E), wherein the fuel gas is contacted in the vessel with a metal or metal ions or another reactant which is capable of reacting with component (E).

With regard to the preferred configuration of the odorants comprising component (E) to be used in this case, reference is made to the foregoing discussion of odorants according to the invention and fuel gases.

Methods which are in practice particularly relevant for odorizing fuel gas having a methane content of at least 60% by weight (preferably natural gas) correspond in their preferred configurations to the particularly preferred odorants according to the invention. Preferably, an odorant according to the invention is added to a fuel gas to be odorized in an amount which causes a warning smell. Amounts of odorant that are preferably to be used, based on the amount of the fuel gas to be odorized, are specified above.

Further aspects of the invention emerge from the appended claims.

The following examples describe the invention. Unless otherwise stated, all particulars relate to weight.

The abbreviations have the following meanings:

MeAc: methyl acrylate; EtAc: ethyl acrylate; THT: tetrahydrothiophene; MeHQ=hydroquinone monomethyl ether; BHT=2,6-di-tert-butyl-p-cresol; TEMPO=2,2,6,6-tetramethylpiperidin-1-oxyl.

EXAMPLES

The odorants according to the invention of the following table 1 were olfactorily assessed in concentrations of 10 and 25 mg/Nm³ of natural gas (natural gas L; methane content: approx. 85% by volume) with regard to their warning smell and their warning intensity against unodorized natural gas (blank value). These concentrations correspond to the typical concentrations of odorant in natural gas under conventional conditions.

The test method was carried out at room temperature (about 20° C.) in such a way that the odorant is introduced into a gas flow in a tube. At the end of this 2 m-long tube (the homogenization takes place within the tube), the issuing odorized gas is olfactorily assessed by a group of trained examiners (8 to 12 persons). The assessment was carried out on a scale of from 1 (very weak/offering very little warning) to 10 (very stark/offering a great deal of warning); the specified values are average values.

In order to examine the stability in storage, the odorants according to the invention were added to natural gas L and the odorized natural gas was olfactorily tested after specific periods of time in storage at 40° C. as described. The criterion for stability in storage was the significant olfactory correspondence of the stored odorized gas to the original warning smell.

The results were substantially identical for the two concentrations examined (10 and 25 mg/Nm³ Gas).

TABLE 1 EtAc MeAc THT BHT [% by [% by [% by [% by Example weight of] weight of] weight of] MeHQ weight of] TEMPO Assessmement 1 92.0 — 7.9985 15 ppm — — 8.5 2 88.0 — 11.9987 13 ppm — — 9.0 3 — 90.0 9.9985 15 ppm — — 8.0 4 60.0 30.0 9.9985 15 ppm — — 9.5 5** 91.0 — 8.8985 15 ppm 0.10 — 9.5 6** 91.0 — 8.9900 15 ppm — 85 ppm 9.5 **greatly improved stability in storage

After a storage time of more than 8 months at 40° C., the warning smell could still be perceived very clearly in all examples 1 to 6.

The odorants according to examples 5 and 6, which comprised BHT or TEMPO, had particularly high stability in storage in the odorized natural gas. Even after a storage time of well over 8 months at 40° C., the warning smell was almost unaltered compared to the freshly odorized natural gas.

SPECIFIC EMBODIMENTS

Specific embodiment one comprises an odorant comprising or consisting of

-   (A) at least 75% by weight of acrylic acid methyl ester and/or     acrylic acid ethyl ester, -   (B) 2-19.5% by weight of tetrahydrothiophene (THT), -   (C) 5-50 ppm of hydroquinone monomethyl ether,     and also neither, one or both components selected from the group     consisting of -   (D) 0.025-0.2% by weight of butylhydroxy toluene and/or butyl     hydroxyanisole     and -   (E) 5-500 ppm of one or more compounds of formula (I)

wherein R is selected from the group consisting of H, —OH, —NH₂, —O₂CR¹ and —NOCR¹, wherein R¹ represents an alkyl radical containing 1 to 4 carbon atoms, based on the total weight of the odorant.

Specific embodiment two comprises the odorant as in specific embodiment one, comprising

-   (D) 0.025-0.2% by weight of butylhydroxy toluene and/or butyl     hydroxyanisole     and/or -   (E) 5-500 ppm of one or more compounds of formula (I)

wherein

-   R is selected from the group consisting of H, —OH, —NH₂, —O₂CR¹ and     —NOCR¹, wherein R¹ represents an alkyl radical containing 1 to 4     carbon atoms.

Specific embodiment three comprises the odorant as in one of the preceding specific embodiments, comprising or consisting of

-   (A) at least 84% by weight of acrylic acid methyl ester and/or     acrylic acid ethyl ester,     and/or -   (B) 5-15% by weight of tetrahydrothiophene (THT),     and/or -   (C) 10-20 ppm of hydroquinone monomethyl ether,     and/or -   (D) 0.05-0.15% by weight of butylhydroxy toluene and/or butyl     hydroxyanisole     and/or -   (E) 10-200 ppm of one or more compounds of formula (I).

Specific embodiment four comprises the odorant as in one of the preceding specific embodiments, comprising

-   (A) at least 84% by weight of acrylic acid methyl ester and/or     acrylic acid ethyl ester, -   (B) 5-15% by weight of tetrahydrothiophene (THT),     and -   (C) 10-20 ppm of hydroquinone monomethyl ether     and also neither, one or both components selected from the group     consisting of -   (D) 0.05-0.15% by weight of butylhydroxy toluene and/or butyl     hydroxyanisole     and -   (E) 10-200 ppm of one or more compounds of formula (I).

Specific embodiment five comprises the odorant as in one of the preceding specific embodiments, comprising in component (E) one or more compounds of formula (I)

wherein R is selected from the group consisting of H and —OH.

Specific embodiment six comprises the odorant as in one of the preceding specific embodiments, comprising

-   (A) at least 84% by weight of acrylic acid methyl ester and/or     acrylic acid ethyl ester, -   (B) 5-15% by weight of tetrahydrothiophene (THT),     and -   (C) 10-20 ppm of hydroquinone monomethyl ether     and also one or both components selected from the group consisting     of -   (D) 0.05-0.15% by weight of butylhydroxy toluene     and -   (E) 10-200 ppm of one or more compounds of formula (I)

wherein R is selected from the group consisting of H and —OH.

Specific embodiment seven comprises the odorant as in one of the preceding specific embodiments, comprising neither tert-butyl mercaptan (TBM) nor ethyl mercaptan.

Specific embodiment eight comprises the odorant as in one of the preceding specific embodiments, wherein the odorant comprises no mercaptan.

Specific embodiment nine comprises the odorant as in one of the preceding specific embodiments, wherein the odorant comprises, apart from tetrahydrothiophene (THT), no sulfur-containing compound.

Specific embodiment ten comprises a fuel gas having a methane content of at least 60% by weight, comprising an odorant as defined in one of the preceding specific embodiments.

Specific embodiment eleven comprises the fuel gas as in specific embodiment ten, characterized in that the fuel gas is natural gas.

Specific embodiment twelve comprises a vessel comprising

(i) an odorant as in one of specific embodiments one to eight, comprising component (E), wherein the odorant or (ii) a fuel gas as in one of specific embodiments nine and ten, containing an odorant comprising component (E), wherein the fuel gas is contacted in the vessel with a metal or metal ions or another reactant which is capable of reacting with component (E). 

1. An odorant comprising or consisting of (A) at least 75% by weight of acrylic acid methyl ester and/or acrylic acid ethyl ester, (B) 2-19.5% by weight of tetrahydrothiophene (THT), (C) 5-50 ppm of hydroquinone monomethyl ether, and also neither, one or both components are selected from the group consisting of (D) 0.025-0.2% by weight of butylhydroxy toluene and/or butyl hydroxyanisole and (E) 5-500 ppm of one or more compounds of formula (I)

wherein R is selected from the group consisting of H, —OH, —NH₂, —O₂CR¹ and —NOCR¹, wherein R¹ represents an alkyl radical containing 1 to 4 carbon atoms, based on the total weight of the odorant.
 2. The odorant as claimed in claim 1, comprising (D) 0.025-0.2% by weight of butylhydroxy toluene and/or butyl hydroxyanisole and/or (E) 5-500 ppm of one or more compounds of formula (I)

wherein R is selected from the group consisting of H, —OH, —NH₂, —O₂CR¹ and —NOCR¹, wherein R¹ represents an alkyl radical containing 1 to 4 carbon atoms.
 3. The odorant as claimed in claim 1, comprising or consisting of (A) at least 84% by weight of acrylic acid methyl ester and/or acrylic acid ethyl ester, and/or (B) 5-15% by weight of tetrahydrothiophene (THT), and/or (C) 10-20 ppm of hydroquinone monomethyl ether, and/or (D) 0.05-0.15% by weight of butylhydroxy toluene and/or butyl hydroxyanisole and/or (E) 10-200 ppm of one or more compounds of formula (I).
 4. The odorant as claimed in claim 1, comprising (A) at least 84% by weight of acrylic acid methyl ester and/or acrylic acid ethyl ester, (B) 5-15% by weight of tetrahydrothiophene (THT), and (C) 10-20 ppm of hydroquinone monomethyl ether and also neither, one or both components selected from the group consisting of (D) 0.05-0.15% by weight of butylhydroxy toluene and/or butyl hydroxyanisole and (E) 10-200 ppm of one or more compounds of formula (I).
 5. The odorant as claimed in claim 1, comprising in component (E) one or more compounds of formula (I)

wherein R is selected from the group consisting of H and —OH.
 6. The odorant as claimed in claim 1, comprising (A) at least 84% by weight of acrylic acid methyl ester and/or acrylic acid ethyl ester, (B) 5-15% by weight of tetrahydrothiophene (THT), and (C) 10-20 ppm of hydroquinone monomethyl ether and also one or both components selected from the group consisting of (D) 0.05-0.15% by weight of butylhydroxy toluene and (E) 10-200 ppm of one or more compounds of formula (I)

wherein R is selected from the group consisting of H and —OH.
 7. The odorant as claimed in claim 1, comprising neither tert-butyl mercaptan (TBM) nor ethyl mercaptan.
 8. The odorant as claimed in claim 1, wherein the odorant comprises no mercaptan.
 9. The odorant as claimed in claim 1, wherein the odorant comprises, apart from tetrahydrothiophene (THT), no sulfur-containing compound.
 10. A fuel gas having a methane content of at least 60% by weight, comprising an odorant as defined in claim
 1. 11. The fuel gas as claimed in claim 10, wherein the fuel gas is natural gas.
 12. A vessel comprising (i) an odorant as claimed in claim 1, comprising component (E), wherein the odorant is contacted in the vessel with a metal or metal ions or another reactant which is capable of reacting with component (E) or (ii) a fuel gas having a methane content of at least 60% by weight, containing an odorant as defined in claim 1 comprising component (E), wherein the fuel gas is contacted in the vessel with a metal or metal ions or another reactant which is capable of reacting with component (E). 